Butyl rubber was one of the earlier synthetic rubbers to be developed. While it quickly replaced other rubbers for use in inner tubes because of its low gas permeability, it was the discovery of halogenated butyl rubbers which lead to the success of tubeless tires. The halogenated butyl rubbers can readily be compounded for effective bonding cures with the tire carcass.
In the manufacture of halogenated butyl rubber residual amounts of isoprene and isobutylene monomer are also halogenated. Where the halogenation is carried out in a solvent, these and other organic halides become concentrated in the solvent, and ultimately the concentration of organic halides in the final rubber product increases.
One of the chlorides produced during the halogenation of butyl rubber is 2-methyl-3-chloropropene (MAC). Because of its volatility characteristics, this compound generally concentrates in the solvent (hexane) used for the chlorination. Where the solvent is used interchangeably for chlorination and bromination of butyl rubber, MAC is converted during the bromination process to 2-methyl-1,2-dibromo-3-chloropropane (MDBCP).
While many of the hydrocarbon halides are objectionable from an environmental standpoint, of particular concern is methyl-dibromo-chloro-propane (MDBCP), a highly toxic, potentially carcinogenic compound, which also may cause male sterility.
Many techniques are known for removing halides from process streams. For example, in the production of methyl chloride and methylene chloride by the (oxy) chlorination of methane, the chlorides can be recovered by gas phase adsorption in beds of adsorbent materials including silica gels, activated carbon, activated aluminum, molecular sieves or their combinations; see U.S. Pat. No. 4,020,117. The adsorption is carried out at about -50.degree. C. to about 20.degree. C. The adsorbed halides are stripped from the adsorption stage at about 100.degree.-400.degree. C.
Similarly, German Pat. No. 2,839,516 discloses a process for purifying an exhaust gas stream to remove contaminants such as halogens or halogenated hydrocarbons by passing the gas through alumina or calcium compounds.
British Pat. No. 1,438,246 discloses a process for reacting a chloroform process stream containing impurities by contacting the stream in the vapor phase with activated carbon or alumina. It is alleged that CH.sub.2 ClBr, which is present as impurities in the chloroform, reacts to form CHCl.sub.2 Br and CH.sub.2 Cl.sub.2, which are then readily separated from the chloroform by distillation.
Soviet Union Pat. No. 506,597 teaches the purification of recycled methylene chloride-isobutylene stream by passing the compounds first in the vapor phase over alumina and then in the liquid phase at 10.degree.-20.degree. C. It is disclosed that the process removes microparticles of water, dimethyl ether and HCl from the stream.
U.S. Pat. No. 2,347,945 discloses a method for removing organic fluorides from a hydrocarbon stream either in the liquid or gaseous phase by contacting the stream with a "contact material." The contact material can be alumina, hydrated bauxite, chromium oxide and metals from the iron groups, especially nickel deposited on an inert support.
U.S. Pat. No. 3,864,243 discloses a process for the removal of combined chlorine (organic or inorganic) from a hydrocarbon stream by percolating the hydrocarbon through a bed of dehydrated activated alumina, e.g., bauxite. The adsorption process is said to be more effective at room temperature than at elevated temperatures, e.g., 98.degree. C. Similarly, U.S. Pat. No. 3,862,900 discloses the room temperature adsorption of organic halides on molecular sieve (pore size 7-11 .ANG.).
U.S. Pat. No. 2,412,220 discloses a process for the removal of organic fluorides from a hydrocarbon stream by passing the hydrocarbon through a bed of alumina which is catalytically active for hydrogenation or dehydrogenation. It is alleged that the effluent stream contains silicon fluorides which are subsequently removed by treating the hydrocarbon stream with an alkali metal hydroxide, e.g., NaOH, and then filtering the hydrocarbon stream through a non-siliceous granular filter medium, e.g., charcoal. In a similar vein, U.S. Pat. No. 2,391,149 discloses the removal of fluorides from a hydrocarbon stream by contacting the hydrocarbon with alumina which has been impregnated with an alkali metal hydroxide.
While the art generally teaches the use of materials such activated carbon and alumina for the purification of halide containing process streams it is apparent from these disclosures that not all organic halides are removed from a process stream contacted with these and other materials of the prior art. Furthermore, there is no disclosure of the removal of methallyl chloride or MDBCP from such hydrocarbon streams; nor is there any teaching from which it would be concluded that a particular contact medium is preferred over others for the removal of methallyl chloride or MDBCP from a hydrocarbon stream.